Don’t read the book Annihilation is based on, if you haven’t already. I’m told that Alex Garland’s film, out February 23, veers considerably from the plot of Jeff VanderMeer’s hit 2014 novel; those going in expecting a faithful adaptation will be disappointed, and may spend the bulk of the movie frustrated about what’s not there instead of appreciating what is. Which would be a shame, because there’s much to savor in the film, a dark and difficult sci-fi thriller about one hell of an existential crisis.

Evoking 2016’s Arrival, the film stars Natalie Portman as a grieving scientist—she’s a biologist who specializes in cancer cell research at Johns Hopkins—who’s called to investigate an extraterrestrial phenomenon. Somewhere on the Gulf Coast, a meteor strike has produced a glowing orb of light—they call it the Shimmer—that has been steadily growing. What’s more alarming is that almost nothing the military has sent into the affected area, drone or human, has returned. But the thing needs to be understood, so Portman’s Lena joins a team of scientists as they trek into harm’s way in search of the truth.

As he showed with his first film, Ex Machina, Garland has an expert sense of how to establish an eerie, enticing world, calibrating dread and allure in just the right measure. Annihilation, which was shot by Rob Hardy, has an ominous beauty; it holds our attention even when we want to look away out of fear or disgust. Past the Shimmer’s translucent walls, the scientists find a verdant place teeming with life. But it’s alive in an altered way; there’s something distinctly off and unnatural about the flora and fauna thriving in this haunted, humanless expanse. As the scientists explore—and realize things are definitely not right—Garland introduces one arresting visual after another, gradually building something almost Lovecraftian in its fantastical horror and awe.

Annihilation is very much about bodies, and to that end Garland does not shy away from gore. There are a couple of moments in the film that are stomach-turningly revolting. (Ugh, stomachs.) But they’re so unflinchingly staged, so blunt about what they’re showing us, that you have to admire them. In order for Annihilation to really drive home its themes, to clarify its stakes, it’s important that we don’t just see the Shimmer creating foreign forms, but also destroying familiar ones. It’s a grim kind of necessity, and though I certainly didn’t have fun watching what Annihilation does to a few of its humans, the gnarly stuff is never gratuitous.

This is a serious, considered film. Though loaded with aesthetic splendor—matching the gorgeous photography is Geoff Barrow and Ben Salisbury’s transfixing score—little in the film feels like an empty flourish. Garland’s disposition is graver, more particular than that, and this makes the film an almost painfully enveloping experience, the landscape so thoroughly realized that it offers near total immersion. I left Annihilation feeling rattled and exhausted—but good rattled, good exhausted. It’s rare that a studio movie dares to engage with an audience in such a somber and probing and insistent way, affording us so little time to breathe or destress or clear our heads.

A particularly engaging facet of the film is that the cast is almost entirely women, with all five scientists played by a well-curated group of actresses. Annihilation isn’t set up as any kind of “go girl,” “strong female character” message movie, but there is some feminist triumph in seeing this kind of story told from an entirely female perspective. Without a baseline assumption of canned male toughness and bravado, the characters in Annihilation are freer to have more a more interesting dynamic—their steeliness and sorrow, their fear and flintiness, intriguingly commingle and inform one another.

Unburdened by the typical clunky character tropes of largely male thrillers or sci-fi films, Annihilation finds new and compelling angles of inquiry. Its humanity is specific, nuanced, more fully realized. There’s something quietly revolutionary about the way the film addresses gender both plainly and coyly, staging another upending of the supposedly natural order in a film that is already doing plenty of that.

Of course, it helps to have the right actresses in the roles. Portman gives her saturnine character a chilly resolve, keeping her at a bit of a distance, only occasionally exposing a raw emotional register. That restraint pays off; Portman joins a hallowed roster of fine actresses who have commandingly anchored arty science-fiction films. Jennifer Jason Leigh is imposing as a sinister psychologist and team leader, a woman clearly possessed of some internal storms but who presents flatly and without affect, only breaking to let out little hisses of acid humor. Gina Rodriguez and Tessa Thompson ably play two friendly younger scientists who—because of the Shimmer, or because of their own secretly troubled minds—gradually reveal darker sides. It’s a particularly startling pleasure to watch Rodriguez work in this mode, traveling miles away from Jane the Virgin.

I was most taken by Swedish actress Tuva Novotny, whose character, Sheppard, emits an otherworldly auric energy. There’s a softness, a kindness to her incisive empathy, but something watchful and suspicious about it, too. It’s not a terribly big role, but Novotny is utterly magnetic whenever she’s on screen, casting a mysterious, mournful glow over her scenes. She’s served well by Garland’s writing, which has an elegant rhythm and cadence that’s a little sideways, a little unnerving. His characters speak maybe too smoothly. (I don’t know how much dialogue is taken from the novel. Apologies to VanderMeer if it’s all his doing.)

All that said, as Annihilation reached its surreal and feverish climax, it began to lose me. I suppose I was just so captivated by the movie’s building unease that the end result was bound to disappoint a little. Couldn’t it just build forever? More concretely, though, I don’t love that in the final scene all of this wonder and madness could, from one interpretation, be reduced to an allegory about relationships torn apart and then repaired, each person different than before, in subtle or profound ways. That feels like a too-neat way to humanize a story that already speaks to plenty of human questions and worries.

But, I also respect the film’s conclusion for all its nervy conviction. Annihilation is a spiritual high-sci-fi fantasia that is admirably committed to its weirdness and solemnity—hard, gloomy stuff made with such rigor and care that the film never feels punishing. Garland is a breathtakingly talented filmmaker, one whose few second-film stumblings—the unwieldy scope of his ambitions, his scrambling for an ending—are forgivable. Annihilation murmurs and roars with ideas, a dense and sad and scary inquest into life and self. It’s a true cinematic experience. And it will be streaming on Netflix in most countries next month.